In the papermaking industry, there is an apparatus which is used to thicken pulp and paper stock. Early on such devices were commonly referred to as deckers. These early devices involved the use of cylinder molds which included a porous cylinder mold rotating in a vat of liquid with a controlled input of slurry. Water would be drained off through the cylinder mold thus thickening the remaining slurry which would be drained off. An example of this type of device can be found in U.S. Pat. No. 4,106,980.
An improvement on the then conventional thickeners can be found in U.S. Pat. No. 4,722,793. This patent describes a device which avoids the use of a cylinder mold. It employs a single pair of smooth-surfaced rolls and a single fabric trained around those rolls so that it wraps substantially 180° of the surface of each roll. The pulp stock to be thickened is initially delivered to the inside of a fabric run approaching the top of one roll so that the pulp is trapped in a zone between the fabric and the roll and is made to travel around the roll with the fabric. Centrifugal force causes liquid to be expressed through the fabric from the pulp trapped between the fabric and the roll.
The resulting partially dewatered pulp then travels on a lower fabric run to the other roll, where it is similarly subjected to centrifugal force causing further expression of liquid through the fabric. After travelling around the surfaces of both rolls, the pulp is removed from the surface of the second roll.
In order to guide the fabric in a path perpendicular to the axes of the two rolls, the fabric was provided along one or both of its edges on its bottom surfaces with a strip of material or guide in the shape of a V-belt. This guide was intended to fit into a peripheral groove in each of the rolls.
This belt is made separate from the fabric and mechanically attached thereto. Due, however, to the high-speed operation of the device, difficulty was encountered in maintaining the guide on the fabric.
In an effort to improve on this arrangement, U.S. Pat. No. 5,039,412 teaches providing for stitching the V-belt guide to the fabric and providing a band of adhesive on the fabric in the area of the stitching. The application of the adhesive extends a short distance inward from the side of the fabric. Also, guides are provided on the outer edge of the fabric so that they are positioned on the outside of the rolls rather than in a groove or grooves in the rolls.
In other industrial belting applications, certain machines have been constructed without any controlled mechanical active guiding system. These types of machines require belt fabrics with very secure v-guides on the wear side for frictional guiding against the outer edges of rolls, or in specific grooves in the rolls machined at either edge or in the center thereof. In addition, the fabric must maintain a low coefficient of friction on its wear side to facilitate machine thread-up.
The current industry standard for these types of machines include permeable fabrics with v-guides secured by one or a combination of the following four methods: 1) sewing the v-guide onto the fabric using various types of monofilament or multifilament threads; 2) gluing the v-guide onto the fabric by choosing appropriate combinations of glue and v-guide materials to create a chemical bond; 3) filling the fabric structure with the same material used to manufacture the v-guide, to create a bond through fusion upon heating and mating both surfaces under pressure; and 4) priming the fabric with a material chemically compatible to that used in the v-guide, so to create a combination of chemical and thermal surface fusion upon mating both structures under heat and pressure.
U.S. Pat. No. 5,039,412 (discussed above), U.S. Pat. Nos. 5,558,926 and 5,840,378 (discussed later) all teach applications of the first, second and third methods. In addition, the fourth method has been and continues to be used in the production of impermeable/solid belting.
Unfortunately, all the above methods have certain drawbacks. For example, the sewing method is susceptible to fatigue failure due to both flexing of the threads, and to the abrasion on the exposed opposite side of the fabric to which the v-guide is attached. On the other hand, the second, third and fourth methods depend on a surface bond between two interfaces, which is a function of both the available surface area as well as the chemical affinity between the two materials. Although methods two through four avoid the abrasion problem of method one, the less than ideal bonding and flex fatigue at the interface may nevertheless impair durability. A related disadvantage is that the bond strength between the fabric and v-guide is always less than the tear strength of either the fabric or v-guide materials alone. This allows for the possibility of v-guide delamination.
In other belt applications, single or multi-ply polyurethane, polyvinyl chloride, or synthetic rubber structures supplied as flat stock are threaded and joined endless on the machine, via either a non-marking pin seam, or via splicing using a time consuming skiving and chemical bonding type process. The high degree of available surface area for bonding on the wear side of these structures makes it possible to attach v-guides using a simple melt fusion process, with or without surface priming (depending on the compatibility between polymer types in the belt and v-guides). However, the disadvantage with this method is, again, that the bond strength is always less than the tear strength of either the belting or v-guide materials alone.
In view of the foregoing, it is desirable to employ a non-marking, pin-seamable fabric in these applications, so to avoid the excessive time and inconvenience of the skiving and bonding process which requires expensive outside contractors to perform this specialized time-consuming process. In this connection, it has been suggested that a coated, spiral fabric might provide an easy-to-pin, non-marking seamable structure. On the other hand, currently available coated spiral structures are difficult to produce with v-guides for two reasons. First, unfilled constructions with less than 0.20 mm plane difference on the v-guide bonding surface exhibit insufficient surface area for fusion bonding. Second, fully filled structures with uniformly smooth bonding surfaces offer little durability advantages over the current standards—again, due to the bond strength being less than the tear strength of either of the two laminates.
Other prior art includes the following:
U.S. Pat. No. 5,466,339 is a conventional seamed papermaking felt. Extruded monofilaments are secured in a machine direction to the underside of the felt in a spaced parallel relation and overlie the area of the seam protecting the seam from abrasion;
U.S. Pat. No. 5,840,378 is an endless woven papermachine belt with an anti-flexing part of thermoplastic resin provided at the edges of the paper side and a guide ridge of thermoplastic resin at the edges of the machine side. The guide ridges are welded integrally with the anti-flexing parts;
U.S. Pat. No. 6,214,752 is a shoe press jacket with a woven base fabric. One surface is coated with resin and the full thickness of the fabric is filled with this resin. A coated layer is formed on the other side;
U.S. Pat. No. 6,465,074 is a resin-impregnated endless extended nip-press or calendar belt with a woven base fabric. This woven fabric includes elements which have been coated with a first polymeric resin material. At least one of the surfaces of the belt is coated with a second polymeric material. The first and second polymers have an affinity for each other so that the second coating establishes a chemical interlock with the elements having the first coating;
U.S. Pat. No. 5,558,926 discloses a bending resistant part of a fabric, formed by filling a polyurethane resin in the internal structure of the fabric. A guide protrusion molded from similar polyurethane is arranged on the bending resistant part by fusion. Cutting caused by bending and wearing of the fabric near the guide protrusion is purportedly prevented;
U.S. Pat. No. 3,523,867 is a wire belt for Fourdrinier machines. On the edges of the belt, woven or cut to width, there are laid up to about ten reinforcing strands, preferably of plastics material. The strands provide reinforcement for the edges and resist damage and cracking, without stiffening the belt unduly or making it thicker;
U.S. Pat. No. 5,384,014 is an apparatus for thickening a suspension of solid particles in liquid. The device employs rolls each having a headbox which delivers a flow of the suspension to be thickened in such manner that it is trapped between the wire and the portion of the roll wrapped by the wire. The trapped suspension is thus dewatered and concentrated by expression of liquid through the wire; and
U.S. Pat. No. 5,731,059 is a dryer fabric formed with a plurality of silicone strips along its edge portions to prevent wear due to abrasion and heat. The silicone rubber encapsulates the end portions and the edges of the yarns, forming beads along the outer surfaces of the dryer fabric which separate the yarns from direct contact with the drums.
While some or all of the foregoing references have certain attendant advantages, further improvements and/or alternative forms, are always desirable.